Grounding pots...yuck

Discussion in 'Luthier's Corner' started by Suburban, Oct 25, 2005.

  1. Suburban


    Jan 15, 2001
    lower mid Sweden
    OK, I admit, I missed totally on the soldering course, OK! :bawl:

    However, I do manage to do a decent work on most connections, i.e. it works, and looks OK. However, grounding the pots seems to be...impossible!?! At least, I have never produced a joint that I was satisfied with.

    Can somebody give a crash course here? Or, better yet, a real tutorial like Wilsers defret thingy - that would be smashing. :hyper:

    I may add that I use a pencil tip solder pen of rather high quality, but without direct temperature control.

    :help: :help: :help:
  2. tjclem

    tjclem Supporting Member Commercial User

    Jun 6, 2004
    Central Florida
    Owner and builder Clementbass
    Flux and a good sized soldering tip. Heat the pot with the flat edge of the iron and get abead of solder to flow on it then attach the wire......t
  3. Sand the back of the pot with a bit of 220 grit. It'll help a lot.
  4. Scott French

    Scott French Dude Supporting Member

    May 12, 2004
    Grass Valley, CA
    I'd never claim to be the prettiest of solderereeres, but I am happy with the strength of my joints. First I get all my gear lined up on a test board {IMAGE 1}. Next I use the flat/hot spot of the iron to put down a pool of solder {IMAGE 2}. Then take a wire that's already been tinned with solder and place it over the pool. Using the hot part of the iron push the wire down into the pool {IMAGE 3}. This heats the wire, the tinned solder and the pool of solder all at the same time and creates a really strong joint.

    Sorry about the rough pics, its tough to solder and take a pic at the same time. I had some wiring to do today anyway but kept forgetting to take a pic at the right time, that's why there's little continuity in these.
  5. Suburban


    Jan 15, 2001
    lower mid Sweden
    Hm, seems I need a bigger solder tip, as a start. And then some of Scott's technique, combined with some sanding... Seems pretty smart.

    But for how long can you heat a pot back?
    I have ruined a few, and I expect it was due to overheating. I.e. overheating the pot inside, though I still couldn't melt the lead on the pot back...
  6. tjclem

    tjclem Supporting Member Commercial User

    Jun 6, 2004
    Central Florida
    Owner and builder Clementbass
    I have never hurt a pot. A larger tip should help heat the area quicker so you won't overheat the whole can........t
  7. nateo

    nateo Schubie Fan #1

    Mar 2, 2003
    Ottawa, Ontario
    You might want to check what kind of solder your using. I've had loads of trouble when accidentally using silver solder, which has a much higher melting point.

    Also, if you've got a high quality iron (read "high power") the tip size shouldn't be a huge problem. Sure it'll work a bit faster if you had a bigger one, but I've soldered some fairly significant parts with a precision tip. It just takes a bit of time.

    One thing you could try is letting your tip heat up without touching anything, then put a dab of solder on it. This should melt just fine (if it doesn't then it's not your technique holding you back). Then when you touch it to the pot the melted solder will give you a much better surface for heat transfer than using a non-wetted tip. Beyond that it's just a matter of patience and waiting for the pot to heat enough to wet.

    I don't claim to be a pro star solder-man, but I've done enough of it to know a few tricks. Believe me when I say that guitar / bass wiring is a whole lot more forgiving than discrete surface mount soldering. Having great big meathooks for hands doesn't help when your biggest component is all of 1 mm long.

  8. Quit bragging. :mad:

    LP pictures coming soon.
  9. +100 this works like a champ...just soldered a new pot into one of my basses...sanded a patch on the pot first...and the solder took to the surface straight away...
  10. fookgub


    Jun 5, 2005
    Houston, TX
    Just to reiterate what others have said, more heat is a good thing here. I used to dread soldering pots with my old 15W pencil. Later I got a 45W iron, and it made life much easier. After that, I got a temperature controlled soldering station, and I'm never going back to pencils or guns! Guitar electronics are VERY forgiving of excess heat... about the worst you'll ever do is melt the inner insulation of a coax cable.

    Anyway, here's a little tip. When I'm grounding to a pot, I tin the lead first, then melt a little pool of solder onto the pot. Then I take some tweezers and push the lead to the solder pool while I heat the joint. After the solder flows evenly, I take the iron off, and contine to hold the wire in place until the solder cools. Works like a champ.

    Also, as others have said, a larger tip can help. I used to like chisel tips for my 45W iron.

    EDIT: Oops.. Looks like Scott already covered my method (and with pictures to boot!). Hey Scott, looks like you've got the same helping hands gizmo as me. I mounted mine to a wood base, and find new uses for it every day. Sure is handy...
  11. seriously...try sandpaper...and yes tinning the wire first well as the solder tip...

    but I've had no problems soldering pots with a 15W pencil tip iron. I use the radio shack (here its Tandy or Dick Smith) variety rosin core 0.8mm solder...
  12. Suburban


    Jan 15, 2001
    lower mid Sweden
    Thanks guys!
    I'm saving this for retroview, since my memory is slightly out of order :D

    This is good info!
  13. All of this so far is right on - here's some of my variations...

    - I use steel wool for my polishing instead of sandpaper. SP makes it look like an amateur has scratched things up. SW makes the pot look like it's chromed! :bassist:

    - I use paste flux. A little dab on the pot before applying the heat and solder will help with the stick. Wipe off the residue after you're done.

    - I will loop the stripped end of the wire into a ring to keep all of the strands and the solder puddle in a small area. I always tin the ends first.

    - An extremely clean iron tip will get the most heat into the work the quickest.

    Nateo's suggestion of tinning the iron for heat transfer is one of the best given yet. That molten glob not only helps heat transfer, it might be the only solder needed for the attachment if the wire is tinned first.
  14. Dugz Ink

    Dugz Ink

    Oct 23, 2005
    If I have to keep the heat low, I usually tin the ends of the wire first, put the heat and solder on whatever the other surface is, then put the wire in place as soon as the solder starts to flow onto the other surface.

    Remove the heat as soon as the solder flows smoothly between the wire and the surface... but hold the wire in place until the solder cools a bit.

    Getting the solder to flow is critical! A "cold solder joint" (two soldered surfaces just stuck together) will be prone to picking up RFI/EMI, and will crack if the guitar gets bumped too hard. (You might know that already, but I think we should point that out for the benefit of other readers.)
  15. kjbrowne


    Jun 14, 2005
    I dont ground to the back of the pot anymore. I use the shielding as a common ground and solder all my grounds to it. If you dont have copper shielding a thin brass plate glued to the inside of the cavity and drilled to match the holes for the pots can be used.
  16. Fealach

    Fealach Guest

    Apr 23, 2003
    Gone to a better place
    So happy I stumbled on this thread. Soldering wires to pots has been the bane of my existence.
  17. fookgub


    Jun 5, 2005
    Houston, TX
    That's good advice. I always use star grounding to the volume pot, but it gets to be a pain when I want to rework something and have to deal with a bunch of wires that have been twisted up and soldered to the back of a pot. I think next time, I'm going to use a solder lug attached to the shield.
  18. Suburban


    Jan 15, 2001
    lower mid Sweden
    Yeah, I've thought about this, too. This would be a rather attractive choice, since I do shielded cavities, and some people say that dual grounding is a bad thing.
    However, some other say that the shield should be kept away from the electronics, except at the jack ground. Being a mechanic, I don't know who to rely on when the electrics get this specific... :(
  19. luknfur


    Jan 14, 2004

    Yep shielding and skip the ground wires. Cleaner, less clutter, less work to do, significantly reduces the chances of inadverantly melting adjacent wires, eliminates the open-back blend control ground issue, you don't have to worry about a less than professional looking solder joint on pot backs - and you'll never have to desolder them for whatever reason.

    The only major functional drawback to shielding is it's ideal for shorts. So wires protruding too far through the lugs or hot lugs close to bay walls are especially prone. I've either taken a piece of electrical tape and put it down under each lug and between a hot lug and bay wall or I've actually just ran about 5/8" strips from pot to pot and turned the pot lugs away from the strips with no other shielding in the cavity.

    I've done the same wiring onboard preamps as outboards using a household metal 4x4 electrical box (controls mounted to 1/8" wood lid) - which is pretty ideal (see Dimento's Onboard Preamp Experiment). All you have to do is connect the pots really, like a ground wire. Just use a meter and verify you have a good connection - but I've never had any problem with shielding strips and I can't say that for soldered grounds.

    Or, if you don't want to shield the hole cavity, you can just do the bay floor and the tape thing then there's no issue with the walls. Don't even have to form fit the floor, just a shape that will connect the pots - the lazy way.

    But if you're going to solder, in my experience you have to have heat and clean surfaces - and sometimes flux. A 15 watt iron won't cut it. You can actually do more damage with a low watt iron for a long period than brief contact with a 500 watt iron.
  20. Dugz Ink

    Dugz Ink

    Oct 23, 2005
    If you mean two ground connections for the pot chassis, then you're correct; that creates a ground loop, which can create noise if there is a difference in resistance bewteen the two grounds.

    You can attach the pot to a piece of metal that is grounded, and the pot is now grounded. It's quick and easy... unless corrosion/oxidation builds up betweeen the two surfaces. If that happens, you'll pick up more RFI/EMI than if the pot chassis wasn't grounded.

    I prefer to attach a wire to the pot, and keep the pot seperated from the shielding. Overkill? Some people think so. But it eleviates a host of protential problems, and all it takes is a nylon washer for each pot, some eletrical tape, a piece of wire, some solder, and your time.

    You can "daisy chain" multiple pots with a common ground wire that connects to your jack ground, eleviating the number of wires that run to the jack.

    As mentioned, it really is smart to cover bare shielding with electrical tape, to eliminate the possibility that a bare connection can touch the shielding. Again, a connection that barely touches will pick up a lot more RFI/EMI, so eliminate that opportunity.

    For related information, see THIS THREAD.